If the workpieces are to be coated with conductive material, such as water-based paint, in many cases the electrostatic atomizers operate in a known way with external charging, such that the atomizer cones or other spraying heads, which are set to a high voltage in direct or contact charging, can be grounded and thus need not be insulated from the grounded paint supply system, which would require the likewise generally known, relatively expensive potential insulation system. In other cases, external charging can also be preferred over direct charging for other reasons or they can be combined, e.g., in order to improve the application efficiency, which is defined as the ratio of the amount of particles deposited on the workpiece to the amount of sprayed particles (DE 4105116).
For a high-speed rotary atomizer of the class mentioned above known from EP 0238031, the needle-shaped electrodes sit in a circular ring body made of insulating material, which surrounds the external housing of the atomizer at a negligible radial distance and for this purpose is held by supports projecting in the radial direction from the external housing. This construction has not proven itself in practice because, among other things, it is too bulky. In addition, attempts have been made to increase the tracking current or surface path between the electrode tips by embedding the electrodes in pins extending like fingers (FIG. 3 of EP 0238031; EP 0283918). In a refinement of this pin construction, for today's conventional atomizers using external discharge, the electrodes are arranged in elongated insulating bodies, which extend from a ring body set directly on a rear part of the external housing in the axial direction towards the workpieces to be coated, wherein here the ionizing ends of the electrodes are also arranged at a considerable radial distance from the outer side of the housing (Dürr/Behr, Technisches Handbuch [Technical Handbook], Einführung in die Technik in die PKW-Lackierung [Introduction to the technology of automobile painting], Apr. 4, 1999; EP 0767005; DE 19909369 etc.). Apart from the fact that only a small number of electrodes can be distributed around the atomizer axis due to construction and other reasons, such as due to cleaning problems, these conventional electrode holder constructions also have the disadvantage that they limit the motion and operation possibilities for coating systems with painting robots due to their bulky outer shape, e.g., because narrow angular or inner regions of the workpieces are hard to reach or cannot be reached at all, or because they hinder the changing of atomizers, which is desired in many coating systems, in automatic changing stations.
Another problem of the known atomizer of the considered type, however, is that most significantly, the electrode tips arranged far outside the spray head in the radial direction tend to become contaminated, particularly through self-coating. This is not only undesired due to the risk of contamination of the workpieces to be coated through paint and other particles that are later freed, but also because the contamination has a negative effect on the electric field, which has the result of reducing the application efficiency and consequently much stronger self-coating. A weakened field can also be caused by overspray particles, i.e., paint droplets which are sprayed past the workpiece and then “stray,” and which can be deposited on the electrode tips of the atomizer moving through the overspray cloud. Due to the weakened field, even more particles can reach the electrodes until finally the ionization of the surrounding air by the corona effect of the electrodes is more or less stopped. In addition, the contamination can lead to electrical arcing and other defects. For these reasons, the electrodes must be regularly cleaned at short time intervals with the result of undesired operating interruptions. The time, work, device, and material expense is also undesired for the cleaning, wherein the mentioned pin-like electrode holder constructions have proven to be a hindrance for both manual and also automatic cleaning.
The invention is based on the problem of presenting an electrostatic atomizer, which is also suitable for coating systems using painting robots, which is as small as possible, and which enables better application efficiency than before in a simple way, particularly without frequent cleaning.
This problem is solved by the features of the claims.